Fractionation control apparatus



Original Filed Deo. lO, l1942 C. G. GERHOLD FRACTIONATION VCOANTRQL' APPARATUS F l. j J7 6 Sheets-Sheet 1 @zza/eraser' Dec. 14, 1948. c. G. GERHOLD 2,455,398

FRACTIONATION CONTROL APPARATUS Original Filed Deo. 10, 1942 6 Sheets-Sheet 2 Dec. M, 1948. Y c; G. GERHOLD 2,456,398

FRACTIONATION coNTRoL APPARATUS Y original Filed Deo. 1o', 1942 e sheds-sheet 3 QV i o gf/47 l V f Dec. 14', 1948. c.l G. GERHOLD FRACTIONATION CONTROL APPARATUS 6 Sheets-Sheet 4 Original Filed DeC.

Dec. 14, 1948. c. G. GERHOLD 2,456,398

FRACTIONATION CONTROL APPARATUS I Original Filed Deo. 10, 1942 6 Shets-Sheet 5 llis Dec. 14, 194s. C. G. GERHQLD 2,456,398

FRA-CTv-IONATIQN CONTROL APPARATUS original Filed Deo. 1o, 1942 l e sheets-sheet 6 FZ? c?.

v f glei/y l atentecl Dec. 14i, 1.948

QFFHCE FRACTIUNATION CONTRL APPARATUS Clarence G. Gerhold, Chicago, Ill., assigner to Universal Oil Products Company, Chica-go, lll., a lcorporation of .Delaware v Original application December l0, 1942, Serial No.

Divided and this application October 27,1944, Serial No. 560,527

' 1o claims. (c1. ics-132) application is fa division of Serial No.

468,509, led December l, l194:2 and nowvabandomed. Y

The invention :relates toiannimproved apparatusifor effecting the separation of selectedccm- Donents :trom e mixture of materials of different boiling points -by `fractional distillation of the mixture. `The invention is particularly advantageous :as appliedto the 4separation of materials having boiling :points ,which are relatively close together and is particularly :intended to iullill a needin the:oilgrenlngindustry for a method and means .of :separating golose-cut, selected fractions from multiple componentmixtures of normally gaseous or normally yliquid hydrocarbons on a commercial scale.

The advent andrapid :adoption of Acatalytic processes iortheoonversion of hydrocarbons, such as, :for *.example, ithe catalytic polymerization of olens, .the catalytic alkyla-tion lof parafilns, aromatics -rsor naphthenes with olens and the vcatalytic :memorization of normal paraffins and olefins. demandnforibestsresults, the fractionation of available :charging materials or products of thee operatiomorfboth, to separate relatively pure selected fraction-s from a mixture comprising components boiling `'relatively close V.to the .boiling point of the desired fraction.

.In many instances the mixture from 4Which the .i desired .fraction lis to be. i separated contains components boiling; only afiew degrees Fahrenheit above and i below fthe boiling 'point of fthe desired `fraction and good separation therebetween is dilcultifif not impossiblazto achieve by vprevious .methods ,which 4are applicable to operation on a commercial scale. Laboratory methods of separating Arelatively .pure vindividual hydrocarbons are, vin most instances, not .applicable to plant operation. 'The present invention. is particularly addressedto the solution of such :problems 'The applicability of the invention to a wide variety of :ifractionating:problems encountered in zvarious-.branchesfof the chemical industries will lie-.apparent to A,those con-versant with the art of .fractional distillation. However', for the V purpose of` illustration, :the subsequent vdescrilzitionwill .be drectedfprincipally to theseparation Yci vhydrocarbons ,fand more :particularly to the separation of normally gaseous hydrocarbons.

The apparatus provided by the invention relies ifor its successfuloperation upon the vaporpressure characteristics-ofthe material vto-be separated, as compared withithe `vapor pressure characteristics lof the .next higher boiling lor next lower boiling pcomponentsof.y the mixture from which its separation is eiected. By controlling the iractonatlng .operation to maintaina substantially constant differential at a selected point in [the fractonating system between the pressure eXertedby the material undergoing fractionation atthatpointfand the .pressure exerted-by arcierence material ofV known vapor pressure char.- acteristics ,at the temperature eXising at said control point in the ractionating system, I am able to recover an overhead or a bottoms product from ,the fractionator fof substantially constant vapor .pressure and accordingly of substantially constant composition. Visual indication of this difference in vapor pressure at the control point may be accomplished by any of several types of instrumentalities which Will be subsequently described. The'control of operating conditions to maintain .a :substantially `constant differential at thenontrol point-may be manual, but in the preierred embodiment of the invention is accomplished'bysuitable automatic control instruments which .willalsobe subsequently described.

The separation of one'or more selected components from ol-mixture of materials of different boiling points by fractional distillation is accomplished, according to conventional methods, in-a fractionating column having three separate controis;A Theseare, (l) control ofthe general operating .temperature-.pressure level,` (2) control of the reiiux vratio and (3) the control which sets the composition of the product by adjustment of the heat land material balance. The .present invention Iinvolves the use of each of these three general controls, but its novelty and advantages reside intimprovements to the third control, above mentioned. i

Intconventionaloperation when it is desired to obtain .an loverhead product of substantially constant composition, the top temperature vof the `iraotionating column is maintained constant Within `relatively close limits, Ii the composition of thebottoms product is to be maintained substantially constant, the bottom temperature of the;fractionating column is maintained constant Within relatively close limits. Thus, separation is leffected ion the basis of dilierence in boiling points between the fraction to be recovered .and the higher vboiling or lower boiling compognentsoof `Athe vmixture undergoing fractionation. Qbyiously, separation on this basis requires the maintenance of `a substantially constant oper- .ating pressure inthe fractionatng column since .boiling :points Vary inpinverse relation toA the 'ration between fractions which boil relatively close together, results from the inability to maintain constant operating pressure within the extremely close limits required for good separation. Pressure iluctuations which cannot be eliminated result from variations in the load'on the fractionating column and inherent imperfections in even l the best pressure control instruments now availay, As a result of such fluctuations in operating ble. pressure, even though they may be small, a controller which maintains constant temperature at the top or at the bottom of the fractionating column actually causes variations in the composition of the .product by faiiure to adjust the temperature to compensate for changes in pressure.

1n contradistinction to the conventional methspeciiic mode of operation provided by the invention but dierent from that employed in the preceding gures.

Figure 4 illustrates a portion of a fractionating column equipped with one specific form of the device provided by the invention for measuring "pressure dierence between the material underod of operation above outlined, the method pro- Y vided by the invention does not involve maintaining a constant temperature at the control point in the fractionating system but adjusts the heat "and material balance in response to minor variations between the pressure exerted by the material undergoing fractionation at the control point andthe pressure exerted by a reference material of known vapor pressure characteristics maintained at a temperature substantially corresponding to that existing in the fractionator at said control point. Due to the approximate parallelism of vapor pressure curves for materials of similar compositions, maintaining a substanf tially constant pressure differential between the reference material of known composition and the material undergoing fractionation gives a much closer approach to maintaining a denite composition gradient between these materials than can be obtained by maintaining a constant ternperature at the control point. With this improved method of control, permissible fluctuations in operating pressure may be quite large and better control than can be obtained by conventional methods is accomplished even when the pressure variations are of a minor nature.

Due to the approximate parallelism between the vapor pressure curves of materials, such as hydrocarbons, of similar chemical composition but different and relatively close boiling point, a considerable leeway is possible in the choice of the'reference material above mentioned. However, the optimum sensitivity and freedom from the effect of changes in operating pressure is attained when the vapor pressure characteristics of the reference material are identical to the vapor pressure characteristics of the material desired inthe fractionating system at the control point. A close approach to this condition is advantageous and, in the preferred embodiment of the invention, the composition of the reference material corresponds vto or closely approaches that of the material which it is desired to maintain in the fractionating system at the control point. It is, however, within the scope of the invention to employ any reference material having vapor pressure characteristics which can be correlated with the vapor pressure characteristics of the material which it is desired to maintain in the ractionating system at the control point.

yThe aforementioned' and other features and advantages of the invention will be apparent with reference to the accompanying diagrammatic` drawing and the following description thereof.

In the drawing Figure 1 illustrates a fractioniating system with controls which permit its operation in the improved manner provided by the invention.

going fractionation within the column and a reference material of predetermined vapor pressure characteristics.

Figure 5 is an enlarged detail of a portion of the apparatus shown in Figure 4.

Figure 6 is another View, shown partially in section, ofthe device illustrated in Figure 5, taken along line 6-6 in Figure 5.

Figure '7 shows a longitudinal section of a portion of the device Aillustrated in Figure 5.

Figure 8 diagrammatically illustrates the importantv features of one specific form of control instrument which may be employed with the device illustrated in Figures 4, 5, 6 and 7 for automatically controlling the operating conditions of the fractionating column in accordance with the lfeatures of the invention.

Figure 9 diagrammatically illustrates a portion of another specific lormv of control instrument which may be utilized, as will be later explained, in accomplishing the improved mode of operation provided by the invention.

Referring now particularly to Figure l, the apparatus here illustrated comprises a fractionating column l5 of any suitable conventional type employing suitable contacting means such as perforated plates, bubble decks or the like, indicated at i5. The mixture to be fractionated is supplied, preferably in heated essentially vaporous or gaseous state, through line IT and valve` I8 to an intermediate' point in the fractionating column and, in the case illustrated, is separated into a liquid bottoms fraction and a lower boiling overhead vaporous or gaseous stream,

i Provision is made for reboiling the bottoms fraction to substantially free the same of undesired light components by directing liquid accumulated in the lower portion of the column through line I9 to reboiler 2B, wherein it is reboiled by passing steam, hot oil, or other suitable heating medium through line 2 I, flow control valve 22, orice 23 and closed coil 24, disposed within the reboiler, in'indirect contact and heat transfer relation with the bottoms supplied to this Zone from the column. The heating medium is discharged from coil 24 through line 25 and the quantity thereof passed through the reboiler is regulated at valve 22 by a flow-control instrument 26 which may be one of any of the several well known types of liow controllers equipped with means for adjusting the control point. One suitable form of this instrument is illustrated lin Figure9 and willbe later described. The refboiled bottoms fraction is discharged from the reboiler through line 21 and valve 28 to cooling :and storage or elsewhere, as desired. Vapors and/or gases evolved in the reboiler are directed therefrom through line 29 back to the lower portion of the fractionating column.

Vapors and/or gases, comprising the relatively light components of the mixture supplied to the better' understanding of thisl preferred type of instrument'. y

`Referring now particularly` to Figures 4, 5, 6 'and '7, an instrument, such as shown at 45 in `Figure land here indicated by the same reference ,.fnumeral, is suitably mounted on a blind flange B which forms a detachable cover-plate;for an vopening 5l provided in the wall of the fractiona- `tor. The fractionator is again designated, as in Figure 1, by the reference numeral I5. The opening .5l is disposed at a selectedpoint in the .columnbetween adjacent bubble trays I6 and, in sthe case illustrated, flanges 50 is detachably bolted to the wall of the columnv or to a pad 52 which is welded or otherwise suitably joined to the cylindrical-walL although a conventional nozzle` or othersuitable means of access to the column may lbe substituted, when desired;l y

The 'element which is sensitive to pressure changes within the column and the means associated therewithfor transmitting movement in this element tothe control instrument 45 -is also 4mounted on flange 50 and is disposed within the `fractionating column, preferably in the vapor pressure-sensitive device will not be affected by eddyV currents `in the liquid or the general move,-

ment of liquid on the tray. In case it is immersed inthe pool of liquid on the tray, I preferably select a zone in the latter which is relatively quiescent n and not too close to a bubble cap or downpipe.

As indicated in Figure 6, the pressure-sensitive element or hydron of the device comprises an Vexternal bellows-like member 54 and .smaller internal bellows-like member 55, each of which is substantially cylindrical in form and is suitably joined in a pressure-tight manner at one end to a stationary, washer-like member 56 and at -its opposite end to a movable, washer-like member 51.

Members 56 and 51 serve to closethe annular space 58 between members 54 and 55 and y this space is partially lled with a suitable ref- .erence fluid, such as previously mentioned, of Aknown vapor pressure characteristics.

Member 56 is bolted, as illustrated, or otherwise suitably securedv to a substantially rigid Vbracket 59 mounted, as illustrated, on flange 50. Member Fil is bolted, as illustrated, or otherwise suitably attached to a memberV 60 which, in the case illuslrtrated, has threeradial arms, each of which extends between a pair of vset screws 6l which serve as stops to limit movement of the free end of the hydron.k The set screws are threaded, in the case illustrated, to suitable` lugs B2 provided on -i the substantially rigid brackets 63 and 64 which, in turn, are mounted, as illustrated, on flange 50.

The exterior surface of bellows-member. 54 and the interior surface of bellows-member 55 are in Contact With the fluid medium comprising, in the case illustrated, the mixture of vapors and/or ,gases prevailing between the adjacent bubble trays.

The exterior surface of bellows member l55 and the interior surfacev of 54 are in vcontact with the reference fluid disposed in space 58 so that the latter is maintained at essentially the same temperature as the vapor or vapor-gas mixture between the trays. l

By providing two bellows-members, arranged as-illustrated, I obtaina high ratio of heater `@transfer surface. to volume for the reference uid ,would act as a heat reservoir.

the provisions for permitting free circulation through the space 65 within the hydronj materially assists in maintaining a negligible temperature difference between the reference fluid and the fluid surrounding the hydron The bellows 54 and 55 are, of course, flexible members formed of relatively light gauge metal, such as, for example, copper, aluminum, stainless steel or other metal or alloy selected to suit the particular conditions of service encountered and I preferably avoid the disposition, close to the bellows-members, of any mass of metal which Thus, a high order of sensitivity is obtained in the hydron, any change in the temperature of the surrounding fluid being quickly transmitted to the reference fluid within the hydron.

Inpperation, any change in the pressure prevailing in the surrounding fluid, as compared with the pressure exerted by the reference fluid within the hydron tends to contract or elongate the hydron, depending upon the direction ofthe change in differential pressure and to a degree corresponding to the magnitude of the change. Thus, expansion of the bellows indicates an increase of the internal pressure in the hydron as compared with the external pressure and contraction of the bellows indicates an increase in the external pressure as compared with the internal pressure. The movement of member 60 with expansion and contraction of the bellowsmembers is transmitted, in the case illustrated, by a flexible metal member 66 to the movable arm 61 of a torsion tube device which translates linear movement of the hydron into rotary movement of shaft 68 (see Figure 5), which extends through flange 50 and into the case of instrument 45 where it is connected by suitable linkage, as will be later described, to the Operating mechanism of the instrument.

The torsion tube device above referred to is a mechanism commonly employed by instrument manufacturers in situations where it is desirable to avoid packing a rotary shaft. Due to the familiarity of those conversant in the art with this type of device, it need not be described here in detail and may within the scope of the invention assume any of its several well known specific forms. A portion of this device is illustrated in detail by the longitudinal cross-section, as shown in Figure 7. A force appliedby movement of the hydron" through the frictionless bearing arrangement '13 (see Figures 4 and 5) imparts a true rotary motion to the inner end 'I4 of the device, causing a slight twist in tube 10 between its inner end of attachment at 'Il to shaft 68, and its outerend, which is attached at 'l2 to sheath 59, the latter being screwed into flange 50 at l5 and held rigid. Thus, shaft SB is rotated through 'a small arc and packing for the shaft where it passes through flange 50 is eliminated, thus obviating a variable resistance to rotation of the 65shaft which would occur if a stuffing box and packing were utilized. v

Since the hydron is extremely sensitive to small changes in differential pressure, its max- I imum movement, as fixed by the stops, will ordinarily be quite small, forl example, of the order of one-tenth of an inch, or thereabouts, and the 'rotational movement of shaft 68 may be of the afi-eases permitted by adjustmentof the=stopstheftension being decreasedaszthehydron expands. Thus, the exible member 6.6, linking member 6l]y on the hydron with arm ii'l,` is always in tension, eliminating the possibility of distortion in this flexible-.member which;4 mighty absorb expansive movementY of thehydron" rather than transmitting-iti to arm. 61;.

One specific.` modification contemplated in. an instrument.v of,- the. sam'e.- general typev illustrated and above.- described; substitutes ay plurality of individual bellows members-or"hydrons"of relatively small diameter for the klargerbellows Maand 5.5' of- Figure 6i In; such; cases.` the' individual small. diameter. hydrons are secured. at, their opposite endsftdmembersfsimilar to'members 59 andri of vFig-ure 6, andzthe individual. hydrons mayxbe. disposed in astraight' line, circle. or any other desired'. geometrical',v arrangement. This will give an. even higherrratio; of; heat transfer surfacefto volume in the.hydrons. andalsoprovidesfor good contact'between; all portions of. the heat transfer surfaces oifthe: hydrons andthe surrounding: Huid.. Alsof by' using; a multiplicity ofsmalldiameter"hydrons; intplace4 ofhydrons 54A and 515:. oflarger diameter, the pressure which the l'iydrons1 willisaf'ely withstand may be sube stantia'lly increasefr without decreasing their flexibility or decreasing: the sensitivity of the device.

The'instrument 45 ofligure'flYI may-"beasimple form1 of indicating orrecording: instrument in which the partially'rotatable-arm;f (see Figure 5) islinked through asuitableflever' arrangement of cunventionalform, noti-illustrated, t0 anindi'- cating pointer or recordingpen; Instruments of this type are familiarftoithose conversant Withthe art andto avoidfunnecessary` complication of the drawing are not here:illustrated:

In the preferred embodiment of the invention, theinstrument 45', withrwhichthe-pressure sensi.-V tive device-off 1 "igures=.4i,y 5, 6 andi'?.y is=-connected-, is ofthe automatic` control type and may comprise any of 'several varietiesofY suchI instruments new available. One of'these, namely, a Taylor "Full'scope recording controller isl shown schematically in Fig-ure Sfand" will now be described'.

The instrument shownin FigureS is ofthe airoperated' type, compressed aiiifor its operation being suppliedi thereto-through line 8U at. a: substantiall'y constant` -pressure vindicated by pressure gauge 8i. The output air line 32.; towhich the indicating pressure gauge 83i`sattached leads, in the case illustrated in Figure 1;. tofinstrument 26`-and` the'air :pressure transmitted. through line S'Zfserves, as will' be later described; to maintain or1 re'adjusty the setl point of instrument 2.a in accordance with. impulses. transmitted to:- instrument: 451 through shaftv 6.8i (see. Figure 5).'.

The recording'pen arm184, which isrigidly attacheditoiarm 85 and'flinkedthrough: leversff and BFI with shaft 68,.indicates'fanrtrecords;. on asuitablechart, not: illustrated.. the f rotational position ofarm Sain term-s of differenceeimpressure. within and vexterior to they hydions f 54 and- 55 1 ofFigure 6; The pointer arinzgwhich is attache-d to the rotatable'gear 85,. indicates onithe: same scale or chart the-z desired diierential ipressureftofbermain.- tained betweenthe'. fluid within. and; that; surrounding: the; hydrorr and. its position. may be adjusted' tcsuitcrequirements by the `rotationfofa suitable knob,znot1 illustrated, which. is attached tozgear 9B, theflatter'being. mesh'ed withzgear 89.

. Se` long; as'ftltre` positions of. pen: 841 and pointer &8 coincide; the :pressure exerted by thematerial undergoing.V fractionation! att thee selected. control point in the fractionating columntbearsthefde.- sired relation tothe-pressure exerted: by thefreference iiuid` within. thehydrons and.` the set point of instrument-2.6:v (Figure 1.) is maintained by the1- air pressure transmittedi theretov from instrument. 45. throughalinef 32; Any deviation in theedesiredr relationship between, the.--pressu1'efex-' erted. by the.- materiali undergoing; fractionation ati the:` control.- point: in.- the fractionating column andthe reference fluid resultsin adeviation' of pen 841irom a. position' coinciding, with that. of pointer. 88 and changes thev air' pressure-transmitted through: line-8.2'- to readjust the-set point of flow controller 26- so that more or less heat, asrequired, is supplied toV the reboiler, thus chang-ingthe heat input tothe fractionating cole umn.A so; asv tobring` the vapor pressurev and' compositioniof the material undergoing fractionation at the control point baciato that desired; ,andzre, turn` pen 84E,` to a.-position.y corresponding to that of pointer 88.

We willnow consider howinstrurnent 45ffunctions'y to v-varythe` airfpressuretransmitted through line 8-2 to. accomplishrthe-abovestatedobject. As.- sumingthat `the pressure-exerted by the; material undergoing fractionation at the control?I point becomes too=high, indicating that` itsi composition isv too light and that less-heat shouldxbe; supplied to. the reboiler, the bellows 54 and 55. of Figure 6'y willY contract, causing shaft 58.-'. to rotate; asv viewed in. Figure 8, in' a: counter-clockwise direc,- tion and causing; pen-8.4130'move-.tothe left away from indicator Y88: This causesarm 85 to:l rotate in!` a clockwisedirection-.about itspivot point 91| so' that. its left-hand. end contacts andV lifts", arm Q2. of. the circular'bailie'- whichis pivotedl at its right-hand. endto geara, asfindicatedat 94. The circular bale- 93 regulatesly thefflow' of. air,- through the'bleed line 95 by variation iny the.- elevational position of the baille-in relationto the; outlet nozzle 9.6i of;l the bleedline. In. the: particular instan-ce being considered, baiile 93 is lifted and. more air flows:through-line 95:and nozzle 95.

Line- 95 iS. pivoted: at" 9.1i and, is connected to line`4 98 which. comnfiunicates.` throughr a. suitable restriction` 9u with; the-input airf line Bil; Line 8f4: also` communicates` through the restriction 99 with. a flexible diaphragm` |00, movement of which; regulates' the position of ball; lill` tot vary theflow ofjair from line-:80, on rthe-upstream side ot restrictionl 99'; through line L02 into the output air line 8:2;- Linev 93-y alsofcommunicates withvthe diaphragm |0:so.that:when.moret air is bled yfrom the';system 'bythe liftingiofibaiiie 93., the air pressure on. diaphragm lt decreases, lowerin'g ball Hill andincreasing. the pressure. in. the air output line. 82; Thev increased air; pressure; in linev 82 adjusts the set point of instrument. 2,6,- as Will be.' later; explained;` to; admit less. heat. to the reboiler andzbringthe vapor pressure and composition; of'.therrnaterialy undergoing. fractionation at. thezcontrol point back to the desired value. ThisV rotates shaft. 68 in; a" clockwise directionh as viewed in Figure'S, returning pen184- to` a position coincidingwithfpointer, 38;. Meanwhile, the auto.- ma-tic-reset mechanism of. instrument 45, which is described below, has lowered nozzle 96 by: the downward movement oiline 95,:so-that the'increasedpressurein the-output air line`8'2 doesnot lreturn to its former valueY when` pen. 8.4l is returned. Thus, instrument 26 operates at its new setting. untilV somev other' change in the conditions prevailing within the fractionating column .func- 0 tion to. readjust: the settingof instrument 26: for

maintaining a lower' or a higher rate of heat input to the reboiler.

Obviously, *when 'a change' opposite to that above described occurs in the fractionator, necessitating increased heat input through the reboiler, instrument 45 functions opposite to the operation above described, reducing the air pressure in line 82 and adjusting the set point of instrument 26 in the opposite direction to give an increased flow of heating medium to the reboiler. l The instrument 45 here illustrated embodies the refinements commonly known as adjustable sensitivity and automatic reset. The provisions of adjustable sensitivity functions to regulate the proportional response of the instrument (i. e., the ratio of output pressure change to the movement of the recording pen or indicator). This is -ordinarily necessary in such applications of automatic control as are herein provided to prevent the instrument from hunting or overcontrolling by reducing its sensitivity. With reduced sensitivity, the position of no-zzle 9G follows the movement of baille 93 to a limited extent. This is accomplished, in the case illustrated, through the adjustable parallelogram arrangement ||l3 which moves to raise and lower line 95. Parallelogram |83 is connected on one side with the bellows or hydron |04 and has an adjustable cam |65 on an adjacent side which contacts line 95 to raise and lower the latter with movement of the parallelogram. An inward eX- tension 82 of the air output line 32 admits air from this line into the case HB5 about the bellows H14` so that when the pressure in line 82 increases, bellows |84 contracts and moves the parallelogram to lift line 95, causing nozzle 96 to follow the upward movement of baiiie 93 and limit the increased air bleed from nozzle 96 so as to reduce the sensitivity of the instrument. When the air pressure in line 82 is decreased, bellows Vlill! expands, causing line S5 and nozzle S6 to be lowered and follow the downward movement of baille 93; v

The feature of automatic reset provided in instrument 45 eliminates the necessity for manually adjusting synchonizing wheel |06, as would otherwise be necessary to compensate for load changes in the fractionator. This feature ernbodies the use of a second bellows member |01, on the inside of bellows member |04, and connection of the space |38 between these bellows members with the output air line through an adjustable needle valve device indicator at |09. With this arrangement the air pressure in the space w8 is equalized at the desired rate with the pressure existing in the space between bellows |04 and case IGS, after any change in the pressure in air output line 32 occurs. Thus, in the operation above described, by the time the pen arm 84 has moved back to a position coinciding with pointer 88, line S5 and nozzle 9B have been lowered by movement of the parallelogram |83 to somewhat below the position which it formerly occupied with reference to baffle 93 before the initial deviation of pen 84 occurred. Thus, the increased air pressure is maintained in line 82 and instrument 26 remains at its new setting.

Referring now to Figure 2, wherein the reference numbers corresponding to those of Figure l indicate corresponding equipment with corresponding functions, the control point setting of flow controller 42', which replaces flow controller 42 of Figure 1, is automatically adjusted by instrument 45, while the flow controller 26',

which replaces flow controller 2G of Figure 1, normally operates at a constant control point setting and has the conventional provisions for manually adjusting the setting. These features of instruments 26 and 42' will be described in more detail in conjunction with Figure 9.

In applying the features of the invention as illustrated in Figure 2, the comparative pressure controller comprising instrument 45 is 1ocated at a relatively high point in the column and functions to vary the ratel at which refluxing and coolingv medium is returned from accumulator 33 to the upper portion of the column. Assuming that a change occurs in the operation of the column which causes the material undergoing fractionation at the control point to lose some of its lighter components and become too heavy, the hydron of the comparative vapor pressure controller will expand due to the decreased pressure about the hydron at the control point and this will reduce the pressure in the air output line 82 which, in this instance, connects instrument 45 with instrument 42'. Thefdecreased air pressure in line 82 will in this instance adjust the set point of ow controller 42 to admit more steam to pump 39 and thus increase the rate of reflux return to the column. This will cause a decrease in the temperature prevailing in the upper portion of the column so that less light material is vaporized from the liquid on the tray at the control point and its vapor pressure and composition returns to the desired value. When a change in the opposite direction occurs at the control point, the pressure in line82 is increased and the set point of instrument 42' is adjusted to decrease the steam supplied to pump 39 and thus decrease the rate of reflux return to the column.

Referring now to Figure 3, parts of the fractionating system corresponding in form and function to th'ose of Figurel are again indicated by corresponding reference numerals.- In this application of the features of vthe invention, the output air line 82 from instrument 45 is con nected with the diaphragmof valve 41 in line 3|) which controls the rate at which the overhead stream of vapors and/or gases is removed from the column or, alternatively, this rate may be controlled by a similar valve 41' in line 3B from the vapor space of the reflux accumulator, in which case the air output line from instrument 45 is connected through line 82A with the diaphragm of valve 41.

The operating pressure of the column is maintained substantially constant by a control instrument H2 which may be an instrument like that illustrated in Figure 8 with a Bourdon tube connected to arm 36 instead of connecting this arm with the shaft 68, the latter being eliminated in this instance. The Bourdon tube is made responsive to the pressure prevailing within the column by the connecting line l I4 leading from a suitable point in the column to the Bourdon tube. Variations in the pressure transmitted through line |i4 to the Bourdon tube varies the pressure in the air output line 3 from instrument H2.V Line I|3 leads to the diaphragm of valve 22 in the line 2| through which the heating medium is suppliedto the reboiler. Thus, when the pressure in the calumn decreases slightly, valve 22 is opened to supply more heat to the column and bring the pressure back to the desired value or, if the operating pressure in the 'column increases, the opening through valve v22 is restricted t0 Supply less heat to the reboiler algemene .t3 and .brin-g thev operating, pressure: of the column backi'to theY desiredI value. i

With a` fairly constant. operating pressure maintained in the column: by instrument-1 2, as above described; instrument fcontro1sf the composition. of lthe material undergoing fractionation at the control point selected, by the opening or closing of valve' 41`or'valve 41 to withdrawy more orless'light material from thetop ofi the column'. Like other forms of pressurecontrollers, instrument ||2 will not holdv an absolutelyA constant operating pressure in the column andthe comparative vapor pressure controller,,comprisinginstrument 45, asin the applications illustrated" in Figures 1 an-d 2, is sensitive to and compensates for whatever variations occur in the operating pressure.

LetY us assume for the sake ofvillustration that the ratio of, light. to heavy. components in ther feed supplied through line Il'. to column |5 of Figure 3 increases'. Sinceheat is being suppliedy to the column; through. the reboiler at a constant.- rate, anincrease in the light components of the feed will .increase vaporization. within the column and this will cause an increase in the operating pressure. Instrument |-|2 then functionsto'reduce the amount offheat being supplied tothe column through the: reboiler" which. will decrease. vapori.- zationzandzbringfthe columnzback` to substantially the;- same operating. pressure as before;I Mean'- while, an increasedquantity of light. components has probably reached the pointt above thev feed inlet to the column at which instrument 45is connectedv and' inl response to the resulting increased' vapor pressure about the hydrons of the vapor pressure controller, thefhydrons contract and cause' instrument 45* to increase the pressure in its air output line 82^and=increase the opening through valve 41 sothatmorelightmaterial is removed overhead from the column andthe composition ofthe materialundergoing fractionation at the control pointireturns. to that which instrument 45 is set to maintain. Also, since the hydronsl of they vapor pressurecontroller are sensitive to minor changes in the-operating pressure of the column, instrument 45 also compensates for the somewhat inaccurate or delayed' operation of instrument ||2. Thus by the functioningjof bothinstrum'ents H2 and 450peration of.' the column is stabilizedA at substantially the same operating pressurer as prevailed before the composition ofthe feed'changed, with armat'erial oigessentially the same composition as previously existedatlthe control point.

The. mechanism of adjusting` the set point lof instruments, such as iiow controller 26 of Figure 1 and ow controller'42' ofFigure-2, for a different flow" rate through therespective lines. 2| and 40; by' impulses transmitted` to these flow controllers through line 82 from instrument 45, will be apparent to those familiar with instrumentation of this general type. 'Ihe ow control instruments may be any one of the several well known forms and an illustration of one of these will sufce to clearly indicate how they may be utilized to obtain the objectives of the invention. For the sake of consistence, we will assume 'that the flow controller employed is one of the Taylor Fullscope controllers equipped with adjustable sensitivity and automatic reset like that illustrated in Figure 8 and described above, except that arm 85 is actuated by the diierence in pressure prevailing on the upstream and downstream sidesforl oricei 23 inthe-casev` of .instrumenttton inthev casezof'. instrument 42.', bythedi-lerencerin pressure; prevailing: on the: upstreaml and.' downstream sidefofforice 4|; this' being. accomplished by. aJ mercury'manometer, interlinked. Bourdon tubes, bellows or.'- the like',I linked;to armBS-inra conventional' manner; not illustrated. The. Hmm control instrument further-differs from that illustrated in Figure v8 in that automatic means-for adjusting'the-controlpoint (i.` e., the differential pressurewhich the instrument isset tolmai'ntain) aref incorporated inthe instrument. Onesuit'- ablemeansof accomplishing this is illustratedi in Figureg which will" now be' described.

In Figure 9u portions of' theinstrumentl corresponding in formand'function to those of Figure 81. are designated by corresponding prime numbers. A` hydron'| 20,*receiving air pressure from theair output line 82:01 instrument 45, is con:- nectedat.its..free. end'by shaftv |2| with one si'de of an,adjustable,.parallelogram I 22., .similar 4tothe parallel'ogram |03 of Figure 8. A connect-rod |23, pivoted atzoneendto, member` 895 of the instrumenti and` pivoted` at,- its. opposite: end, toa side of. the -parallelogram adjacent .that to which shaft |'2| is'attached, connectstheparallelogfram |122 tofmemb'er 89.-"in such a manner thatian increase in. the. pressure transmitted: tot` hydron |20 through: lineV 82 resets the position of. member 8.9;' to: give. af higher pressure. in` the i airoutput line from. tlieinstrumentand vice versa. Thus, in instrument 2li,v of.: Figure 1, an increased pressureitransmittedthrough-.linex82 to` the adjusting mechanism` comprisingy hydron |203 and'` paralt lelogram |22 will increase the pressure inlthe' air output line from this-instrument to valve 22' and, this' valve beingdirect' acting, the opening therethrough isthusv reducedL to decrease the' supply of^"heat'to the reboiler; As applied to instrument 42' ofiFi'gureZ; increased pressurein line 82 resets instrument 412" to give increased pressureV in the air output line from this 4instrumentto' valve 44'. In this case, valve 4'4 is also. direct-acting, the increased pressure on the' diaphragm serving izo-close the .valve and decrease the flow of'steam topump. 39,.V thereby slowing down the pump and decreasing the ow ofrerl'uxing medium through line .40 tothe.. top of` the. column.

I.A claim as my invention.:

Ina tractionating column, vthe combination of a variablevolume closedchamber disposed at a: selected` control point. within. said columnA and containing aimed.4 quantity of a. reference4 fluid oiknownfvapor pressure` characteristics, vthe volume. ofV saidi chamber being variablein re.- sponse to variations; in differential` pressure .betweenftheiinside and outside of the chamber, and means-for.- adjusting the pressure-diierentialbetweenl the intr-:riory and exterior of. said. cham.- ber,vr inresponse to, changes in volume ,of5 `said chamber.

2. In a fractionating column, the combination of a variable volume Closed chamber disposed at a selected control point wit-hin said column and containing a fixed quantity of a reference fluid of known vapor pressure characteristics, the volume of said chamber being variable in response to variations in diierential pressure between the inside and outside of the chamber, and means for varying the temperature at said selected control point in response to changes in volume of said chamber.

3. In a fractionating column, the combination of a variable volume closed chamber disposed at selectedfcontrolpoint"within said. column and containing a fixed quantity of a'reference fluid of known vapor -pressure, characteristics', the volume of said chamber' beingvariable in responsel to'variations in differential pressure betweeny the' inside' and outside of the chamber, and means for regulating the pressure at said `selected controlf-point in response to changes in volurne of saidchamber. ,i v

4. In a fractionating column, `the combination of a Variable volume closed chamber disposed at a selected control point within saidcolumn and containinga fixed quantity of a reference iluid of known Vapor pressure lcl'iaracteristics, the volume offsaidchamber being variable in response -to `variations in diierential pressure between the inside and outside of the chamber, an adjustable Valve in a vheating material supply line to said fractionating column, means for transposing changes in volumeof said chamber into impulses, and means fory transmitting said impulses to said adjustable Valve for varyingthe latter. A 4` 5. In a fractionating column, the combination `of a variable volume closed chamber disposed at a selected control point withinfsaid column and containing a xed quantity of a reference fluid lof known vapor pressure characteristics, the volume of said chamber being variable in response tovariations in differential pressure between the inside and outside of the chamber, an adjustable valve in a reflux line to said fractionatingcolumn, means for transposing changes in volume of said chamber into impulses and means for transmitting' said impulses to said .adjustable valve for'varying the latter.

6. In a fractionating column, the combination of a variable volume closed chamber disposed at aselected control point within said column and containing a fixed quantity of` a reference fluid ofl known Vvapor pressure characteristics, the `volume, of said chamber being Variable in response to Variations in differential pressure between the inside and outside of the chamber, an adjustable Valve in a vapor line from said column, means for transposing changes in volume 'of saidv chamber intoV impulses and means for transmitting said impulses tosaid adjustable valve for Varying the latter,

7. In a fractionating column, the combination of an annular variable volume closed chamber containing a fixed quantity of a reference fluid of :known Vapor pressure characteristics and comprising r.spaced Ainner and` outer concentric, flexible bellows-like walls, said annular chamber being so arranged within the fractionating column to permit circulation of fluid undergoing fractionation around said outer wall and through the inner cylindrical space formed by said inner wall, and means for adjusting the pressure differential between the interior and exteriorl of said chamber in response to Varia tions in Volume of the chamber, i

G0 Number 8.v In a fractional-,ing column, the combination of an annular variable Volume closed chamber containing a xed quantity of a reference fluid of known vapor pressure characteristics and comprising spaced inner and outer concentric, ilexible bellows-like Walls, said annular chamber being so arranged within the ractionating column to permit circulation of iiuid undergoing fractionation around said outer wall and through the inner cylindricalspace formed by said inner wall, and means for varying the temperature in the columnin response to changes in volume of said chamber.

9. In a ractionating column, the combination of an annular variable Volume closed chamber containing a fixed quantity of a reference uid of known vapor pressure characteristics' and comprising spaced Yinner and outer concentric, flexible bellows-,like walls, said annular chamber beingsoarranged within the fractionating column to permit circulation of iluid undergoing fractionation around said outer wall and through the inner cylindrical space formed by said'inn'er wall, and means for regulating the pressure in the column in response to changes in Volume of said chamber.

10. In a fractionating column, the combination of an annularvariable volume closed chamber containing a xed quantityofv a reference fluid of known vapor pressure characteristics and comprising spaced inner and outer-concentric, ilexible bellows-like walls, said annular chamber being so arranged within the fractionating coiumn to permit circulation of fluid undergoing fractionation around said outer wall and through theinner cylindrical space formed by said inner Wall, means for introducing a reiuxing liquid to the upper portion of the column, and means for regulating the supply of refiuxing liquid to the column in response to changes in Volume of said chamber.

- CLARENCE G. GERI-IOLD.

REFERENCES CITED The following references are of record in the lile of this patent:

UNITED STATES PATENTS Name Date Quinby Jan. 19, 1932 Purdy v June 13, 1933 Peterkin Jan. 9, 1934 Affleck Sept. 15, 1936 Smith Mar. 16, 1937 Kallam July 13, 1937 Hamilton Apr. 30, 1940 Carney Sept. 29, 1942 FOREIGN PATENTS Country Date Great Britain June 23, 1927 Number 

